The sustainable city, a concept that started in the 1970s as an “eco-city” movement that sought to build cities in balance with nature [1], is now generally defined as a city that exerts minimal damage on the environment while maintaining a diverse and resilient economy, an equitable distribution of resources, and a means of citizen participation. On all of these fronts—diversity, equity, engagement—small-scale urbanism is thought to have a better alignment with sustainability goals than large-scale urbanism [2]. Following the work of Jane Jacobs [3], urbanists have been promulgating the benefits of small-scale urbanism, denouncing the liabilities of large-scale form and arguing that neighborhoods that develop or redevelop on a small scale are the ones that are the most sustainable and resilient [4]. Large-scale urban developments—“mega-projects” in the form of town centers, university campuses, and other large format urban schemes—are viewed as antithetical to Jane Jacobs’ brand of incremental change, and the very opposite of a resilient and sustainable city ^[5][6][5,6].

While scale is an essential factor in discussions about sustainable cities, there is no common understanding of what scale is or how it should be measured. Is it about buildings, lots, and block sizes? Is it about single vs. corporate ownership of land? Is it about the geographical distances between points? Cities are aggregations of all of these elements —small lots with single family homes, 200-acre parcels with multi-use buildings with thousands of square feet, and infrastructure and public spaces ranging from intimate to vast. The variation of the scale of urbanism from small to large creates a multitude of effects and experiences.

2. The Scale of Urbanism

Cities have long developed at multiple scales simultaneously, for different purposes and with different effects. Large-scale development was an expression of political power, of absolutism, or of the centralizing force of an authoritarian regime. Monumental scale is a natural fit for authority and control, presupposing an “unentangled decision-making process” and expressing that the ruling authority has the necessary power to get things done [7] (p. 217). Alongside this larger scale, small-scale urban fabric was created and recreated by individual owners, developers of various sizes, and builders working in a more incremental manner. Urban change was accomplished lot by lot, block by block, through the work of many individual owners rather than despots, governments, or large developers [8]. A few important studies have attempted to document these scale changes. Warner and Whittemore [8] chart the evolution of an imagined U.S. city amalgamized from Boston, Philadelphia, and New York. They describe how, through the mid-18th century, most dwellings were small in part due to the high costs of construction. Even in the early streetcar era of massive rowhouse neighborhood expansion, most were built by craftsman at a rate of three to six per year, yet a homogeneity of style tended to develop outside of legal regulation. Hunter categorizes homes into three types: freestanding, attached, and apartments, and charts their evolution as forms in the American landscape [9]. Scheer expands this typology to include not just non-residential buildings, but also patterns of land subdivision, and emphasizes how historical patterns may constrain redevelopment possibilities [10]. Beyond historical analysis, the literature on scale has focused on debating the pros and cons of different scales. Debates about the effect of scale go back at least to the foundations of the field of planning, particularly in the U.S., when Daniel Burnham’s famously declared “make no little plans, for they fail to stir the hearts of men” [11]. Proponents of large development argue that this is the scale at which jobs are generated, infrastructure is financed, and city revenues are increased. The impulse to “go big” in city planning was further promulgated by modernist concepts of urbanism promoted through planners and architects associated with the Congres Internationaux d’Architecture Moderne, known as CIAM [12]. The large scale of modernist towers and freeway schemes prompted Jane Jacobs, among others, to castigate planners [3]. Mid-twentieth century urban renewal (Figure 1) was done at a large scale around the globe, and resulted in widespread displacement. In the U.S., large-scale urban renewal was often directed at African-Americans, prompting further debate about the issue of scale. Relatedly, Jacobs included the scale of finance in her critique, praising the benefits of “gradual money” over the deleterious effects of the “cataclysmic money” inherent in most large plans [3] (p. 291–317). These debates evolved into the 1970s economics of “Small is Beautiful” [13] and calls for informal incremental development as a solution to housing in the developing world [14]. In the 1980s and 1990s, scale debates pinned urban-minded preservationists as small-scale revitalizers working against status quo over-sized suburban sprawl and large “public−private” development schemes ^[15][16][15,16]. As the preservationists worked to revitalize disinvested urban areas, others called for zoning reform to allow small, multi-unit buildings ^[17][18][17,18]. Urban designers ^{[19][20][21][22]}[19,20,21,22] argued that small-scale urbanism was not only more visually appealing and experientially rewarding, but it was better able to support diverse economic and social activity. The New Urbanist movement pitched itself as a champion of small-scale urbanism battling large-scale development that they regarded as an enabler of car-based urban form [23]. While the benefits of small-scale—and the negative impact of large-scale—urbanism were widely recognized by the end of the 20th century, large-scale urbanism continued. This was partly a consequence of boosterish claims about the return of central cities ^{[24][25][26][27]}[24,25,26,27], which stimulated larger-scale private investment in inner-city sites, often enticed by municipal subsidies [28]. Some cities, such as Vancouver, B.C., attempted to infuse urban placemaking principles in these new large-scale developments [29]. Yet the large scale—in both physical form and in terms of the aggregation of finance and capital—was critiqued for contributing to an affordability crisis ^[30][31][30,31] and for creating a global homogenized urban aesthetic irrespective of local conditions [32]. Projects often ran over budget and failed to provide the affordable housing and municipal revenue proponents had claimed ^[33][34][33,34]. The term “mega-project” entered the lexicon as a descriptor of the expanding scale of city building. Flyvbjerg, Bruzelius, and Rothengatter [35] loosely define mega-projects as those over USD 1 billion in costs with a focus on infrastructure. Fainstein and others define mega-projects as “very big, mixed-use developments [that cities use] as attractors of multinational business and sites for new housing,” [32] (p. 768); see also ^[36][37][36,37]. These projects are often built on obsolete or under-utilized industrial land, a distinction from the residential displacement associated with mid-twentieth century urban renewal [38]. There is a perception that these recent mega-projects are “lacking the layering of old and new, small and big, that gives central cities their ambiance and opportunities”, [32] (p. 783), and urbanists have turned their attention to the benefits of “human-scale”—which is mostly “small-scale”—development. Research on urban morphogenesis (the processes that shape the physical form of cities over time) and urban morphology (patterns, typologies, and configurations of urban form) ties into these interests because scale is a significant aspect of the analytical approach. For example, Hillier and Hanson [39] analyzed spatial configuration, including pattern and scale, to understand the relationship between form and function. Busquets [40] examined Barcelona’s urban morphology to understand how it contributes to a human-scale environment. Research on cities like Copenhagen, Amsterdam, and Paris have explored the successful implementation of policies and design strategies that enhance human-scale qualities and promote active modes of transportation, which often translates to what would be considered “small-scale” urbanism ^[41][42][41,42]. Jan Gehl [43] studied the relationship between urban design and human behavior, emphasizing the importance of creating pedestrian-friendly environments and human-scale interventions aimed at increasing social interaction, healthier lifestyles, and improved overall urban livability. Appreciation of small-scale urban form has translated to practice in several ways. Some focus on temporary and smaller-than-a-building scale “Tactical” or Do-It-Yourself (DIY) interventions ^[2][44][2,44]. Others looks for ways to encourage and support small-scale development through developer trainings and networks, such as the Incremental Development Alliance (incrementaldevelopment.org) or through advocacy, research, and consultancy (smalldevelopmentcounts.org; recastcity.com). These advocates argue that the current development milieu accommodates single-family detached housing and larger buildings over four stories, but thwarts “Missing Middle” smaller-scale development that falls in between ^[17][45][17,45]. There has been some focus on the regulatory and financial barriers small-scale urbanism endures [5]. Others have focused on the integrated role small-scale manufacturing can play toward revitalization [46]; see also [47]. Another theme advanced by proponents is the greater affordability and thereby equity that could be achieved through increasing the housing supply with small-scale development. Relatedly, proponents tout small, incremental development [4] and small-scale main street businesses [48] with integrated manufacturing [46] as tools towards building more vibrant, equitable communities. This small-scale urbanism is often positioned, both implicitly and explicitly, as either a more equitable alternative to large-scale capital and subsidy-intensive mega-projects, or a neglected co-contributor to urban vitality. Critics from the left point to the racialized social construction of housing values that would nevertheless persist [49]; for a response to the critique, see [50]. There are also critiques of incremental urbanism for its inability to redress inequities ^[51][52][51,52]. Large-scale social housing, if done right, is still not ruled out as an appropriate scale at which to solve the affordability crisis ^[53][54][55][53,54,55]. These large-scale private developments are often subsidized. In the U.S., this is done through Tax Increment Financing (TIF), a financing tool that allows administrators to pay for programs with future tax revenues generated within a TIF district (an area that has demonstrated “blight” conditions). The property taxes from the TIF district are fixed for a certain period of time (often 20 years), and tax growth above the fixed base level is diverted away from general revenue capture toward a separate TIF district fund (the difference in revenue is the tax increment). The subsidies are justified as necessary to both attract investment to desired areas and mobilize the large amounts of capital required for public infrastructure and amenities. Proponents claim that these subsidized, large-scale developments create jobs, tax revenues, and infrastructure investments that could never be generated in an incremental fashion. U.S. city governments are much more focused on subsidizing large-scale private developments in the name of revitalization, justified as necessary for mobilizing the large amounts of capital needed for public infrastructure and amenities. But critics argue that TIFs and the mega-scale they tend to be associated with are a form of corporate subsidy, used as a cost-free instrument to secure deals with corporations, frequently in areas that do not need supplementary public support [56]. Common examples of TIF use in Chicago include the subsidization of corporate headquarter relocation or renovation, the provision of general support and monetary incentives for private companies, and upscale development in and around the economically advantaged downtown area (the “Loop”). For example, United Airlines received USD 31 million to relocate to downtown Chicago, CNA received USD 13.7 million to renovate its headquarters, and Carbide and Carbon received USD 8.5 million to renovate the Hard Rock Hotel [57]. While not a TIF specifically, the outcry against and eventual rejection of New York City’s bid for Amazon’s H2Q suggest that public and professional opinion on the efficacy of government-subsidized mega-projects as a planning strategy may be shifting [58].